Media gateways need to know when they should accept and reject communication sessions to maintain a specified quality level. Voice over Internet Protocol (VoIP) gateways, for example, should be able to determine when additional calls can be admitted to a network without degrading voice quality for conversations. While modern voice codecs can deal with loss and jitter, there are bounds on these quality measures that can impact a service.
Currently available Traffic Engineering (TE) solutions establish pre-computed bandwidth thresholds that are negotiated network-wide, such that if all thresholds from all gateway circuits are honored, voice quality in a communication network will be sufficient. Asynchronous Transfer Mode (ATM), Multi-Protocol Label Switching (MPLS), Time Division Multiplexing (TDM), and other circuit-based approaches create a static mesh of circuits between all the gateways and assign bandwidth and delay thresholds to those circuits. Quality of Service (QoS) thresholds can be soft bounds that are renegotiated in the event the QoS requirements of a gateway exceed the circuit parameters.
One problem with these approaches is that they add tremendous complexity without directly addressing the root problem, i.e., how to make call admission decisions based on the impact of a given call being set up. TE systems are suited to User Network Interface (UNI) service delivery points and leased line services where a negotiated limit needs to be set and enforced. The goal of TE is assignment of resources based on negotiated or anticipated needs, not optimization of network utilization and QoS differentiation in real time in ad-hoc packet switched systems, for example.
TE solutions also require a homogeneous network. Admission control elements and intermediate equipment must inter-operate in these solutions, thereby binding success of a gateway-based admission control mechanism to the successful deployment of the infrastructure to support it.
In addition, currently available TE solutions do not respond dynamically to actual network conditions. Instead, they assume that all expected bandwidths between end user equipment can be pre-computed. TE solutions thus approximate bandwidth and delay measures and do not rely on real measurements of the actual network at the time a call is to be routed.
Reliable traffic profiles are required for accurate estimates and effective operation of TE systems. Certain call types such as voice with echo suppression and variable compression, however, do not have well defined profiles. Therefore, TE approaches often apply averaging over large numbers of connections, but there is always error. Defining profiles for every possible type of call can also be time consuming and thus can add cost to a system.
In the context of pre-computed versus actual bandwidth, TE approaches do not monitor actual bandwidth usage and availability, as they only track bandwidth that has been previously allocated and, through renegotiation, what could be increased. Allocated bandwidth is considered to be unavailable, regardless of whether that bandwidth is actually used. This can be undesirable since total network bandwidth can be limited by physical infrastructure or Virtual Private Network (VPN) limits, for example.
Similarly, circuit/path bandwidth availability calculations may not reflect actual available bandwidth. These calculations may indicate that pre-computed bandwidth has run out even though the network may still support bandwidth usage and thus additional sessions.
Pre-computation also relies on a specific current network topology. When failures occur, actual topology may change and these calculations are no longer valid. Failover mechanisms may attempt to find alternate routes in the event of simple network failures, for example. TE call admission would ultimately still rely on the former topology, however, and not the topology after any failure(s).
Overbooking in circuit systems is often enabled to provide statistical multiplexing gain. Hard TE limits are thus not useful and might be “softened” in some implementations. This is a result of the fact that real traffic often does not conform to the engineered profiles that TE systems rely on. In this scenario, TE degenerates to QoS differentiation in the datapaths, using such techniques as prioritization or Weighted Fair Queuing (WFQ).
Based on the premise that service revenues are not gained by rejecting communication sessions, it is generally desirable to maximize the number of sessions that communication system infrastructure can support at all times. Thus, there remains a need for improved communication session admission control techniques.